1. Field of the Invention
The present invention relates to a document processing apparatus having means for erasing character data which was recorded and output.
2. Related Background Art
Hitherto, in an electronic typewriter or the like, particularly, in a document having a sequential print mode or the like, an apparatus for erasing the printed characters has been known. In the case of a printer such as impact printer, thermal copy transfer printer, or the like using a recording section of the type for copy transferring the ink of an ink ribbon onto a recording paper, the printed characters are erased by a method whereby the ink which was copy transferred onto the recording paper is peeled off or shaded or the like.
On the other hand, in an apparatus such that character data is stored and buffered into a memory on a unit basis of the line, page, or the like and the buffered characters are edited and, thereafter, they are printed, the information such as kind, print, and the like of the character data can be known in accordance with the content in the memory. Therefore, a technique to erase by giving such information to a printing mechanism has been known.
Although the erasing method by the printing mechanism differs depending on the printing system, the system for thermally copy transferring the ink from the ink ribbon by using a thermal head uses the following two kinds of methods. Consideration will now be made with respect to the case where a character C ("F") has already been printed on a recording paper P as shown in FIG. 5A and this character is erased.
1) A font pattern of a character B as shown in FIG. 5B (hereinafter, such a font pattern is referred to as a box font) which was thickened by turning on eight dots surrounding each dot of the dot pattern (hereinafter, referred to as a font) of the printed character C stored in the memory is made. The thermal head is positioned over the character C. The portion of the thermal head corresponding to the character C is heated by using the box font and the ink is peeled off from the recording paper P.
2) As shown in FIG. 5C, the thermal head is positioned over the character C by using the dot pattern (hereinafter, such a dot pattern is referred to as an area-erasing font) which is derived by turning on all of the dots in a range of the character C on the basis of the character width and height thereof with reference to the content of the memory. Then, the ink is peeled off from the whole character print area by the thermal head.
The above two erasing methods by the thermal copy transfer system have the following problems.
First, in the case of using the box font as shown in FIG. 5B, since the box font is formed by using the data of the ordinary character font for printing, it takes a relatively long time. On the other hand although it is also possible to use a font memory only for use of the box font, in this case, a large memory capacity is needed only to erase. Further, in the case where a plurality of characters were superimposed and printed at the same position on the recording paper or in the case where a plurality of characters were superimposed and printed at point positions which are slightly shifted, there are problems such that it takes time for a process to erase the superimposed characters printed at the same print position one character by one and a part of the recording paper is overlappingly peeled off, so that the printing quality deteriorates.
In the case of using the area-erasing font, there are the following problems. First, since the heating area of the thermal head is wide, electric power consumption is large. Therefore, a voltage drop occurs depending on a power source impedance and the sufficient erasure cannot be executed. On the other hand, in an apparatus which is driven by a battery or the like, the life of the battery is short. Further, since the paper in the portion where no ink is deposited is also peeled off, there is also a problem such that if a character of a small dot density of the font was erased, the recording quality of the recording paper deteriorates or the like.